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P. Roig

Publications and source records attributed to P. Roig.

46 records · Page 3Linked to original sources
arXiv2013

Constraining the Hadronic Contributions to the Muon Anomalous Magnetic Moment

The mini-proceedings of the Workshop on "Constraining the hadronic contributions to the muon anomalous magnetic moment" which included the "13th meeting of the Radio MonteCarLow WG" and the "Satellite meeting R-Measurements at BES-III" held in Trento from April 10th to 12th, 2013, are presented. This collaboration meeting aims to bring together the experimental e+e- collider communities from BaBar, Belle, BESIII, CMD2, KLOE, and SND, with theorists working in the fields of meson transitions form factors, hadronic contributions to (g-2)_μand effective fine structure constant, and development of Monte Carlo generator and Radiative Corrections for precision e+e- and tau physics.

hep-ph↗
arXiv2013

Resonance chiral Lagrangian currents and tau decay Monte Carlo

Measurements of tau lepton, because of its long lifetime, large mass and parity sensitive couplings lead to broad physics interest. From the perspective of high-energy experiments such as at LHC, knowledge of tau lepton properties offers an important ingredient of new physics signatures. From the perspective of lower energies, tau lepton decays constitute an excellent laboratory for hadronic interactions. At present,hundreds of millions of tau decays have been amassed by both Belle and BaBar experiments. It is of utmost importance to represent such data in a form as useful for general applications as possible. In the present paper we describe the set of form factors for hadronic tau decays based on Resonance Chiral Theory. The technical implementation of the form factors in FORTRAN code is also explained. It is shown how it can be installed into TAUOLA Monte Carlo program. Then it is rather easy to implement into software environments of not only Belle and BaBar collaborations but also for FORTRAN and C++ applications of LHC. Description of the current for each tau decay mode is complemented with technical numerical tests. The set is ready for fits, parameters to be used in fits are explained. Arrangements to work with the experimental data not requiring unfolding are prepared. Hadronic currents, ready for confrontation with the tau decay data, but not yet ready for the general use, cover more than 88% of hadronic tau decay width.

hep-ph↗
arXiv2012

Theoretical inputs and errors in the new hadronic currents in TAUOLA

The new hadronic currents implemented in the TAUOLA library are obtained in the unified and consistent framework of Resonance Chiral Theory: a Lagrangian approach in which the resonances exchanged in the hadronic tau decays are active degrees of freedom included in a way that reproduces the low-energy results of Chiral Perturbation Theory. The short-distance QCD constraints on the imaginary part of the spin-one correlators yield relations among the couplings that render the theory predictive. In this communication, the obtaining of the two- and three-meson form factors is sketched. One of the criticisms to our framework is that the error may be as large as 1/3, since it is a realization of the large-N_C limit of QCD in a meson theory. A number of arguments are given which disfavor that claim pointing to smaller errors, which would explain the phenomenological success of our description in these decays. Finally, other minor sources of error and current improvements of the code are discussed.

hep-ph↗
arXiv2010

$τ^-\toηπ^-π^0ν_τ$ and $σ(e^+e^-\to ηπ^+π^-)$ at low energies

We analyze the hadronization structure of $τ\to ηπ^- π^0 ν_τ$ decays. In the isospin limit only the vector current contributes to this process. We compute the relevant form factor within Resonance Chiral Theory, at leading order in the $1/N_C$ expansion, and considering only the contribution of the lightest vector resonances. The couplings in the resonance theory are constrained by imposing the asymptotic behaviour of vector spectral functions ruled by $QCD$. We reproduce the branching ratio of this mode and predict the low-energy behaviour of $σ\left(e^+e^-\toηπ^+π^-\right)$ using isospin symmetry.

hep-ph↗
arXiv2010

Hadron structure in tau -> KKpi nu_tau decays

We analyse the hadronization structure of both vector and axial-vector currents leading to tau -> KKpi nu_tau decays. At leading order in the 1/Nc expansion, and considering only the contribution of the lightest resonances, we work out, within the framework of the resonance chiral Lagrangian, the structure of the local vertices involved in those processes. The couplings in the resonance theory are constrained by imposing the asymptotic behaviour of vector and axial-vector spectral functions ruled by QCD. In this way we predict the hadron spectra and conclude that, contrarily to previous assertions, the vector contribution dominates by far over the axial-vector one in all KKpi charge channels.

hep-ph↗
arXiv2010

tau -> pi pi pi nu_tau decays and the a_1(1260) off-shell width revisited

The tau -> pi pi pi nu_tau decay is driven by the hadronization of the axial-vector current. Within the resonance chiral theory, and considering the large-Nc expansion, this process has been studied in Ref.[1]. In the light of later developments we revise here this previous work by including a new off-shell width for the lightest a_1 resonance that provides a good description of the tau -> pi pi pi nu_tau spectrum and branching ratio. We also consider the role of the rho(1450) resonance in these observables. Thus we bring in an overall description of the tau -> pi pi pi nu_tau process in excellent agreement with our present experimental knowledge.

hep-ph↗
arXiv2009

Quest for precision in hadronic cross sections at low energy: Monte Carlo tools vs. experimental data

We present the achievements of the last years of the experimental and theoretical groups working on hadronic cross section measurements at the low energy e+e- colliders in Beijing, Frascati, Ithaca, Novosibirsk, Stanford and Tsukuba and on tau decays. We sketch the prospects in these fields for the years to come. We emphasise the status and the precision of the Monte Carlo generators used to analyse the hadronic cross section measurements obtained as well with energy scans as with radiative return, to determine luminosities and tau decays. The radiative corrections fully or approximately implemented in the various codes and the contribution of the vacuum polarisation are discussed.

hep-ph↗
arXiv2009

Hadronic tau decays into two and three meson modes within Resonance Chiral Theory

We study two and three meson decays of the tau lepton within the framework of the Resonance Chiral Theory, that is based on the following properties of QCD: its chiral symmetry in the massless case, its large-N_C limit, and the asymptotic behaviour it demands to the relevant form factors. Most of the couplings in the Lagrangian are determined this way rendering the theory predictive. Our outcomes can be tested thanks to the combination of a very good experimental effort (current and forthcoming, at B- and tau-charm-factories) and the very accurate devoted Monte Carlo generators.

hep-ph↗
arXiv2009

Hadronization in three meson channels at tau decays and e+e- cross-section

The hadronic form factors in semileptonic decays of the tau and low-energy e+ e- scattering into hadrons can be described accounting for the following fundamental features: the right chiral structure at low energies, the large-N_C limit of QCD and the known asymptotic behaviour of the theory. All these characteristics are implemented within our approach to the accuracy and within the limits discussed below. Our results -improved with respect to those shown in the talk (they correspond to the ones presented in the V Working Group on Generators for Low-Energy Physics held in Frascati the 6th and 7th of April, 2009) are compared to data for tau to 3pi nu_tau. Our setup in the vector current has been checked (using CVC) with e+e- to KKpi data. We predict the hadronic spectra in all tau to KKpi nu_tau charge modes. Our hadronic matrix elements are being included in the TAUOLA library and may be useful for the experimental collaborations that are analysing tau decays (BaBar and Belle) and to those that will join this effort in the future (BES, super-B factories, LHC and future colliders).

hep-ph↗